The present invention relates to a method for the determination of the concentration of silane gas in a gaseous mixture or in the atmospheric air or, more particularly, to a method for the determination of a relatively low concentration of silane gas in a working gaseous mixture or in the atmospheric air of the working environment as is sometimes used or encountered in the manufacturing process of semiconductor devices.
As is well known, silane SiH.sub.4 is an important material used in a gaseous form in various processes of manufacturing of semiconductor devices. Accordingly, it is important to accurately determine the concentration of silane in a working gas used in the process. ue to the high vapor pressure, furthermore, it is usual that the atmospheric air of the working environment using silane contains the silane more or less so that, in view of the toxicity and inflammability thereof, it is eagerly desired in the semiconductor industry to develop a simple and highly sensitive method for the determination of the silane gas in a gaseous mixture or in air in a relatively low concentration capable of giving reliable results.
Several methods therefor are already known and practiced in the prior art including (1) the electrochemical sensor method using, for example, a membrane Galvani cell or potentiostatic electrolytic cell utilizing the oxidation-reduction reaction of the gas on the surface of the electrode, (2) the chemical reaction-atomic absorption spectrophotometric method in which the silane gas is reacted with mercury oxide to reduce the mercury oxide into vapor of metallic mercury of which the concentration is determined by the atomic absorption spectrophotometry and converted into the concentration of the silane gas, and (3) the chemical luminescence method utilizing the luminescence emitted by the reaction of the silane gas and ozone. These prior art methods, however, have problems and are not quite satisfactory from the standpoint of practice because the sensitivity is not always high enough, selectivity is poor and strongly toxic reagents must be used.
The inventor has previously proposed an apparatus for the concentration determination of several kinds of reactive gases, such as arsine, phosphine, stibine, germane and selenium hydride, used in the processing of semiconductor devices in air, of which the principle of determination utilizes the scattering of light by the fine suspended particles in the air produced when a gaseous mixture of the reactive gas and oxygen is irradiated with ultraviolet. This apparatus and the method, however, are not applicable to the concentration determination of silane gas in a gaseous mixture because the principle thereof is the irradiation of a gaseous mixture of the reactive processing gas and oxygen with ultraviolet, by which the silane gas is not rapidly reacted with oxygen, especially, when the concentration thereof is low.